fetch-gnu.sh: remove incorrect exit 0 (pass tests/cat/splice)

[oech3]

No description provided.

[github-actions]

Binary size comparison:

Individual binary size comparison VS main (threshold: >=5% AND >=4 KB).

Total size of compared binaries: 148.93 MB (+316 KB, +0.21%)

Significant per-binary changes:
  install     1.24 MB ->    1.32 MB  (+80 KB, +6.29%)
  mkdir       1.09 MB ->    1.17 MB  (+80 KB, +7.14%)
  mkfifo      1.09 MB ->    1.16 MB  (+76 KB, +6.83%)
  mknod       1.09 MB ->    1.17 MB  (+76 KB, +6.79%)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/misc/io-errors (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/tail-n0f (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cat/splice is no longer failing!